The art of stereoscopic drawing was devised at least as early as around the year 1600 by the Italian artist Giovanni Battista della Porta. However, until the development of the Wheatstone stereoscope, such pictures could not be any larger than the interpupillary distance; that is a separation of the human eyes of approximately 6.5 centimeters. Various stereoscopic viewers, that is stereoscopes, have been developed since Wheatstone, but the primary object has always been to view stereo pairs mounted at a fixed or nearly fixed distance from the viewers eyes.
The Spanish Surrealist artist Salvador Dali has recently developed a new area of art: stereo paintings. Dali has produced several pairs of paintings that are apparently identical at first glance, but which are actually right and left-eyed stereo views of the subject of the painting. In addition to incorporating the normal stereo perspective differences between the two paintings that one must have for a true stereo pair, Dali has also added subtle variations in lighting and coloring to the two paintings. These are sometimes deliberately exaggerated or distorted so as to induce visual illusions that go beyond realism to the surreal.
In some cases, these stereo paintings are produced with the aid of photographs of models taken from different vantage points; in other cases, by means of extensive foreshortening and parallax calculations. In any event, Dali put an extraordinary amount of effort, attention to detail, and imagination into the creation of these stereo paintings. Clearly this effort deserves a viewing device that allows the viewer to experience stereo fusion without any significant optical degradation of the paintings.
One might approach this design problem in a variety of ways. What is desired are devices that are held up to the eyes in order to view the paintings from any distance, under normal illumination. A viewer should be capable of mass production (several thousand units) to be sold with a limited edition printing of lithographs made from one of Dali's stereo painting pairs.
FIGS. 1 and 2 show the basic problem. The paintings or lithographs are mounted side by side on a wall at eye level. The observer is several feet away and looks between the two paintings. The optics in front of each eye must deviate the line of sight so that the right eye sees only the right-eyed-view painting and the left eye sees only the left-eyed-view painting. To the observer, the two paintings will appear to occupy the same space, and stereo fusion will occur. FIG. 1 shows one way to deviate the lines of sight, and FIG. 2 shows an equally valid alternative.
The constraints affecting the design of the viewer are:
(A) highest possible optical quality; PA1 (B) lowest possible cost; PA1 (C) small size and weight; PA1 (D) no development time--stock optics if at all possible; PA1 (E) Aesthetic compatibility with artistic goals.
In addition, it is desirable to make the viewer adjustable so that the observer will not have to be at a fixed distance from the paintings. The constraint most emphasized is E above--aesthetics. The viewer is itself intended to be a work of art that will reflect certain artistic themes of Dali. Some viewer candidates were rejected solely because of aesthetic failings.
The first viewer considered was a pair of prismatic wedges, shown in FIG. 3. The lines of sight could be deviated in or out. For a reasonable viewing distance, the prism wedge angle must be at least 20.degree., with 30.degree. more like the desired amount. The deviation is fixed in this viewer, so one must stand at a fixed distance from the paintings. Once fusion has been achieved, the brain is very forgiving of small changes in this distance. Still, an adjustable viewer is preferred.